Extreme uv radiation light source device

ABSTRACT

An extreme ultraviolet light source device includes a raw material supplying mechanism. The raw material supplying mechanism includes a disk-shaped rotor, a motor for causing the rotor to rotate, a cover-shaped structure surrounding the rotor via a gap, and a first reservoir provided inside the cover-shaped structure for reserving a liquid high temperature plasma raw material. When the rotor rotates, a portion of the surface on the rotor becomes coated with the liquid high temperature plasma raw material. A portion of the cover-shaped structure has an aperture exposing that surface of the rotor which coated with the high temperature plasma raw material. The high temperature plasma raw material is irradiated with an energy beam from an energy beam supply device through the aperture, and generates EUV radiation.

TECHNICAL FIELD

The present invention relates to an extreme UV (ultraviolet) radiationlight source device, and more particularly an extreme UV radiation lightsource device that includes a raw material supplying mechanism to supplya liquid or solid raw material in order to emit extreme UV light fromlaser-produced plasma.

BACKGROUND ART

As semiconductor integrated circuits are designed in a fine structureand/or in a highly integrated manner, there is a demand for improvingresolution (resolution power) of a projection exposure device that isused to manufacture such semiconductor integrated circuits. To meet suchdemand, a light source for exposure tends to have an even shorterwavelength. As a next generation light source for exposure ofsemiconductor, which comes after an excimer laser device, an extremeultraviolet (EUV) light source device is studied. Such light sourcedevice can emit extreme ultraviolet light at a wavelength between 13 nmand 14 nm, particularly 13.5 nm. The EUV light source device is alsoused as a light source for inspecting (testing) a mask used for aprojection exposure device that uses EUV light.

There are some known methods for the EUV light source device to generate(emit) the extreme ultraviolet light. One of the known methods heats anEUV radiation species (seed) for excitation. This generates a hightemperature plasma. Then, the extreme ultraviolet (EUV) light isradiated and extracted from the high temperature plasma.

One kind of the EUV light source devices that employ such method is adischarge produced plasma (DPP) type EUV light source device. The DPPtype EUV light source device utilizes the EUV radiation light from thehigh temperature plasma generated when the EUV light source device isdriven with an electric current.

Li (lithium) and Sn (tin) draw attention as radiation species (seed)that are used by the EUV light source device to emit an EVU light at awavelength of 13.5 nm and having a strong radiation intensity. In otherwords, Li and Sn draw attention as the high temperature plasma rawmaterial for producing the EUV. The mechanism of the EUV radiation thatrelies upon the DPP method will be described briefly below.

According to the DPP method, electrodes are placed in, for example, adischarge vessel, and the discharge vessel is filled with a raw materialgas (i.e., gaseous high temperature plasma raw material atmosphere).Then, discharge is caused to take place between the electrodes in thehigh temperature plasma raw material atmosphere so as to produce initialplasma. A self magnetic field results from an electric current thatflows between the electrodes upon the discharging, and causes theinitial plasma to shrink. As a result, the density of the initial plasmaincreases, and the plasma temperature steeply rises. This phenomenon isreferred to as “pinch effect” hereinafter. Heating caused by the pincheffect elevates the plasma temperature. The ion density of the high(elevated) temperature plasma is 10¹⁷ to 10²⁰ cm⁻³, and the electrontemperature reaches approximately 20 to 30 eV. Then, the EUV light isemitted from the high temperature plasma.

In recent years, the DPP type EUV light source device uses solid orliquid Sn or solid or liquid Li. The solid or liquid Sn or Li issupplied to the surfaces of the electrodes, across which the dischargetakes place, and irradiated with an energy beam such a laser beam forvaporization. Subsequently, the high temperature plasma is generated bythe discharging. This is proposed in Patent Literature 1 (JapanesePatent Application Laid-Open Publication No. 2007-505460). The followingdescription deals with when the energy beam is a laser beam. This methodis referred to as “LDP” method or “laser assisted gas discharge producedplasma” method in this specification.

Now, an LDP type EUV light source device disclosed in Patent Literature1 (Japanese Patent Application Laid-Open Publication No. 2007-505460)will be described. FIG. 11 of the accompanying drawings shows across-sectional view of the EUV light source device disclosed in PatentLiterature 1 (Japanese Patent Application Laid-Open Publication No.2007-505460).

Reference numerals 114 and 116 designate disk-like electrodes. Theelectrodes 114 and 116 are disposed in a discharge space 112. The innerpressure of the discharge space 112 is regulated to a predeterminedpressure. The electrodes 114 and 116 are spaced from each other by apredetermined distance, and rotate about rotation axes 146,respectively. Reference numeral 124 designates a high temperature plasmaraw material 124 to emit EUV light at a wavelength of 13.5 nm. The hightemperature plasma raw material 124 is a heated and melted metal, e.g.,liquid tin, and is received in containers 126. The temperature of themelted metal 124 is regulated by a temperature adjusting unit 130disposed in each of the containers 126.

The electrodes 114 and 116 are partially immersed in the melted metal124 in the associated containers 126, respectively. The melted metal 124that rides on the surface of each of the electrodes 114 and 116 is movedinto the discharge space 112 upon rotation of the electrode 114, 116.The melted metal 124 which is conveyed into the discharge space 112,i.e., the melted metal 124 present on the surface of each of theelectrodes 114 and 116 which are spaced from each other by thepredetermined distance in the discharge space 112, is irradiated withthe laser beam 120 emitted from a laser irradiation device (not shown).Upon irradiation with the laser beam 120, the melted metal 124 isvaporized.

While the melted metal 124 14 is being vaporized, a pulse electric poweris applied to the electrodes 114 and 116. Thus, a pulse discharge istriggered in the discharge space 112, and a plasma 122 is produced. Alarge current is caused to flow upon the discharging. The large currentheats and excites the plasma 112 such that the plasma temperature iselevated. As a result, the EUV radiation (EUV light) is generated fromthe high temperature plasma. The EUV radiation is taken out in the upperdirection in the drawing.

Therefore, when the LDP method described in Patent Literature 1(Japanese Patent Application Laid-Open Publication No. 2007-505460) isused, the solid or liquid target (high temperature plasma raw material)is irradiated with a laser beam, and the raw material is gasified(vaporized) to produce a gaseous high temperature plasma raw materialatmosphere (initial plasma). Similar to the DPP method, the ion densityin the initial plasma is, for example, approximately 10¹⁶ cm⁻³, and theelectron temperature is, for example, approximately 1 eV or lower than 1eV. Subsequently, the plasma temperature is elevated with the heatingtriggered by the discharge current drive. The ion density in this hightemperature plasma becomes approximately 10¹⁷ cm⁻³ to 10²⁰ cm⁻³, and theelectron temperature becomes approximately 20 eV to 30 eV. As such, thishigh temperature plasma emits the EUV. Similar to the DPP method,therefore, the heating triggered by the discharge current drive in theLDP method, which is disclosed in Patent Literature 1 (Japanese PatentApplication Laid-Open Publication No. 2007-505460), takes advantage ofthe pinch effect.

Reference numeral 148 designates a capacitor bank, which corresponds toa power source. The capacitor bank 148 is electrically connected to themelted metal 124, which is received in each of the containers 126, viainsulated feed lines 150. Because the melted metal 124 is conductive,the electric energy is supplied to the electrodes 114 and 116, which arepartly immersed in the melted metal 124, from the capacitor bank 148 viathe melted metal 124.

According to this method, it is easy to vaporize tin or lithium, whichis solid at room temperature, in the vicinity of the discharge regionwhere the discharge takes place. Specifically, it is possible toefficiently feed the vaporized tin or lithium to the discharge region,and therefore it becomes possible to efficiently extract the EUVradiation at the wavelength of 13.5 nm after the discharging.

The EUV light source device disclosed in Patent Literature 1 (JapanesePatent Application Laid-Open Publication No. 2007-505460) has thefollowing advantages because the electrodes are caused to rotate.

-   -   (i) It is possible to always feed a solid or liquid high        temperature plasma raw material to the discharge region. The        high temperature plasma raw material is a new EUV producing        species (seeds).

(ii) Because that position on each electrode surface, which isirradiated with the laser beam, and the position of the high temperatureplasma generation (position of the discharge part) always change, thethermal load on each electrode reduces, and therefore it is possible toreduce or prevent the wear of the electrodes.

An EUV light source device that uses another method is an LPP (LaserProduced Plasma) type EUV light source device. A mechanism forgenerating the EUV radiation on the basis of the LPP method will bedescribed briefly below.

When the LPP method is used, a target is irradiated with a driver laserbeam to produce the plasma. The material of the target is the hightemperature plasma raw material that can generate the EUV. Similar tothe LDP method, Li (lithium) and Sn (tin) draw attention as the materialof the target. An EUV light source device that relies upon the LPPmethod, which is disclosed in Patent Literature 2 (Japanese PatentApplication Laid-Open Publication No. 2007-529869), will be describedbelow.

FIG. 12 of the accompanying drawings shows a conceptual view of thelaser produced plasma EUV light source 220, which is illustrated in FIG.1 of Patent Literature 2 (Japanese Patent Application Laid-OpenPublication No. 2007-529869). The driver laser for generating the plasmamay include a pulse laser system 222 (e.g., gas discharge excimer laserthat is driven with high power and high pulse repeating frequency), aCO₂ laser or a fluorine molecule laser.

The pulse laser system 222 is, for example, a gas discharge laser systemthat has a master oscillator power amplifier (MOPA) structure. The gasdischarge laser system includes, for example, an oscillator laser system244 and an amplifier laser system 248. The pulse laser system 222 hasmagnetic reactor switching type pulse compressing and timing circuits250 and 252, and pulse power timing monitoring systems 254 and 256.

The light source 220 may also include a target conveying system 224 thatconveys the target in the form of, for example, a droplet, a solidparticle, or a solid particle contained in a droplet. The target may beconveyed into, for example, a chamber 226 by the target conveying system224. The target may also be conveyed to an irradiation site 228, whichis also known as an ignition site, by the target conveying system 224.Although not described in detail here, a system controller 260 conductsthe control such that the target is irradiated with a laser pulse fromthe pulse laser system 222 along a laser beam axis 255 when the targetis in a predetermined location.

The device disclosed in Patent Literature 2 (Japanese Patent ApplicationLaid-Open Publication No. 2007-529869) detects a location of the targetwith, for example, droplet photographing (videotaping) devices 270, 272and 274. Then, a feedback system 262 for detecting the target locationis used to calculate the location and moving path (locus) of the target.Based on these pieces of information, the system controller 260 controlsthe position and direction of the laser beam. A target conveyancecontrolling system 290 corrects the releasing point of the targetdroplet 294, which is released by the target conveying mechanism 292, inresponse to a signal from the system controller 260.

In recent years, as described above, the target material is usuallysupplied in the form of droplet. The LPP method disclosed in PatentLiterature 2 (Japanese Patent Application Laid-Open Publication No.2007-529869) is believed to provide a light source that has powerscalability and produces less debris (clean light source).

Such target conveying system needs to control the droplet size as wellas, in terms of space and time, the laser beam irradiation position, andthe feeding of the droplet. Such control is likely to be affected bydisturbances, i.e., the temperature elevation caused by the plasma, andscattering of the target material and its residual upon the laser beamirradiation. The detail of such control system is described in PatentLiterature 2 (Japanese Patent Application Laid-Open Publication No.2007-529869).

It is said that the LPP method properly controls the target and createsless debris. However, it is recently said that even the LPP methodexerts a large (unneglectable) influence on optical components when theLPP method intend to provide an output required from a semiconductormanufacturing process.

To date, the researches show that both of the LDP method and the LPPmethod use liquid tin (Sn) when a raw material for the high temperatureplasma is supplied to generate EUV radiation. However, the LDP methodhas problems. Namely, scattering of tin and releasing of the electrodematerials occur during vaporization of the raw material upon laser beamirradiation and discharge.

In the LPP method, which is considered to be a cleaner method than theLDP method, the tin scatters when the droplets are produced and the tinis irradiated with the laser beam. This produces a considerable amountof particles and ions, which deteriorate the life of the optical system.These particles and ions are called debris. When the output of the EUVradiation is enhanced, the debris is produced in a larger amount. Thisbecomes a cause of significantly deteriorating the life of those opticalcomponents which are disposed downstream of the light emitting point.

LISTING OF REFERENCES Patent Literatures

-   PATENT LITERATURE 1: Japanese Patent Application Laid-Open    Publication No. 2007-505460-   PATENT LITERATURE 2: Japanese Patent Application Laid-Open    Publication No. 2007-529869-   PATENT LITERATURE 3: PCT International Publication No. 2009/077943-   PATENT LITERATURE 4: Japanese Patent Application Laid-Open    Publication No. 2007-5124-   PATENT LITERATURE 5: Japanese Patent Application Laid-Open    Publication No. 2005-17274-   PATENT LITERATURE 6: Japanese Patent Application Laid-Open    Publication No. 2010-514214-   PATENT LITERATURE 7: Japanese Patent Application Laid-Open    Publication No. 2012-235043

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

The problems of the conventional ways of supplying the high temperatureplasma raw material will be summarized below.

Firstly, use of the solid target is proposed in the method of supplyingthe high temperature plasma raw material for the EUV light source. Whenthis method is used in the DPP method, the discharge electrodesthemselves are made from the solid high temperature plasma raw material.When this method is used in the LPP method, the solid high temperatureplasma raw material, which is prepared, for example, in the form ofwire, is disposed as the target for the laser beam.

This raw material supplying method does not need a complicatedmechanism. However, when this raw material supplying method is used inthe DPP method, the discharge electrodes are worn down upon thedischarge, and the distance between the electrodes changes. This resultsin unstable EUV generation in a long run. When this raw materialsupplying method is used in the LPP method, the material is damaged bythe laser beam when the material is irradiated with the laser beam.Therefore, it is difficult to supply the raw material for a long time.

In addition, the light emitting part (plasma generating portion) isdifficult to cool. Accordingly, it is difficult to suppress the wearingout of the electrodes in the DPP method, and suppress the damage to thetarget due to the heat in the LPP method.

Next, use of the gas target is proposed in the LPP method. This methodof supplying a raw material includes supplying a xenon gas or avaporized or gaseous tin, which is a high temperature plasma rawmaterial, from a nozzle into a EUV generation chamber in the form of agas jet. The gas jet is irradiated with a driver laser beam for plasmageneration. Unlike the solid target, this raw material supplying methoddoes not suffer from a problem of wearing out of the material becausethe high temperature plasma raw material is supplied in the form of gasjet in this raw material supplying method.

It is necessary to expel that portion of the supplied gas jet of thehigh temperature plasma raw material, which does not contribute to theEUV generation. Specifically, unlike the solid target, this raw materialsupplying method requires a nozzle for supplying the gaseous hightemperature plasma raw material, and a separate gas-expelling mechanismfor expelling the gaseous high temperature plasma raw material.

However, part of the gas that contains the vaporized tin, for example,is liquefied and solidified in the EUV generation chamber, and thereforeit is difficult to expel the high temperature plasma raw material.

In addition, because the gas jet spreads after it is injected from thenozzle, it is difficult to locally supply the high temperature plasmaraw material. When the gas jet is irradiated with the driver laser beam,it is impossible to generate a small plasma for light emission (smalllight-emitting plasma).

Furthermore, it is difficult to cool the nozzle, which is located in thevicinity of the high temperature plasma. Thus, the nozzle itself islikely to be damaged.

On the other hand, one of the raw material supplying methods that arecurrently practiced in the LDP method is disclosed in Patent Literature1 (Japanese Patent Application Laid-Open Publication No. 2007-505460).This raw material supplying method includes immersing disc-shapedelectrodes in tin tanks, respectively, and causing the electrodes torotate such that each of the electrodes is coated with a thin film ofthe liquid tin, and the plasma raw material is introduced to the lightemission point. This raw material supplying method introduces the tin asthe plasma raw material, while cooling the electrodes and surroundingcomponents with the liquid tin. However, this raw material supplyingmethod needs an increased electric power and entails an increased amountof tin that contributes to the light emission. An amount of tine to beapplied onto the rotating electrode(s) is limited by the rotating speedof the electrode concerned. This is because the rotation speed of theelectrode needs to be increased in order to smoothly introduce the tinto the plasma, but this creates another problem, i.e., a centrifugalforce increases with the increasing rotation speed of the electrode, andthe increased centrifugal force causes the tin on the rotating electrodeto scatter in the discharge space. Also, it is difficult to maintain thegood contact (wettability) between the electrode and the tin whenforming a thin film of tin on the electrode material.

Another raw material supplying method that is currently practiced inconnection with the LPP method is a droplet method disclosed in PatentLiterature 2 (Japanese Patent Application Laid-Open Publication No.2007-529869). Because this raw material supplying method uses adispersed (discrete) target, the device becomes complicated.Specifically, the device becomes complicated because the target isdifficult to synchronize with the excitation source (driver laser beamfor plasma generation) in terms of time and space, the target isdifficult to have a small size, the luminous efficacy drops if thetarget has an excessively small size, heat generation of the lightemitting part influences a droplet producing device, and high pressuresuch as about 200 atmospheric pressure is needed to release the droplet.Variations in the material feeding in terms of time and space make itdifficult to stably supply the material. Thus, the dose control isdifficult. In addition, the tin and its ion scatter when the target isirradiated with the laser beam, in the same manner as theabove-described raw material supplying method that uses the rotatingelectrodes.

Still another method of supplying the high temperature plasma rawmaterial in the LPP method is disclosed in Patent Literature 3 (PCTInternational Publication No. 2009/077943). Patent Literature 3 (PCTInternational Publication No. 2009/077943) uses disc-shaped rotatingelements (rotors), which are partly immersed in the liquid hightemperature plasma raw material, as a mechanism for supplying the hightemperature plasma raw material.

A half of each rotating element is received in a metallic block having asemicircular recess with a predetermined gap. The liquid hightemperature plasma raw material is supplied to the gap by a liquidconveying unit such as a pump. In this manner, the liquid hightemperature plasma raw material is applied onto each of the rotatingelements. The liquid high temperature plasma raw material is appliedonto the rotating element with a substantially uniform thickness, whichcorresponds to the gap. The applied high temperature plasma raw materialmoves upon rotations of the rotating element such that the raw materialis conveyed to the radiation position of the driver laser beam forplasma generation and the raw material is irradiated with the driverlaser beam. As a result, the EUV radiation (light emission) takes place.

In this raw material supplying method, the feeding of the hightemperature plasma raw material is continuous, unlike the dispersed(discontinued) target used in the droplet method. Thus, stable feedingof the high temperature plasma raw material is realized. However,scattering of the high temperature plasma raw material (tin) uponradiation of the driver laser beam for plasma generation and scatteringof its ion occur in the same manner as the above-described hightemperature plasma raw material supplying methods.

In other words, none of the above-described methods can avoid thegeneration of the debris. In general, therefore, a debris regulationdevice, which is disclosed in Patent Literature 4 (Japanese PatentApplication Laid-Open No. 2007-5124), is provided to prevent the debrisfrom arriving at the downstream optical system and the scanner (opticalsystem for testing a mask if the mask testing device should be protectedfrom the debris: Patent Literature 7 or Japanese Patent ApplicationLaid-Open Publication No. 2012-235043). Debris regulation devices whichare proposed to date cannot completely remove (eliminate) the generateddebris. There is a demand for a method of further reducing an amount ofdebris to be generated.

A semiconductor manufacturing process, which is a primary processcarried out with the EUV generation device, requires approximately 100 Wor more of EUV output. The above-described countermeasure to the debrisis one of quite important issues in order to reduce the frequency ofoptical part exchange and stably operate the light source device.

In view of the problems related to the debris that is generated upon thefeeding of the high temperature plasma raw material and the plasmageneration, an object of the present invention is to provide an extremeultraviolet light source device that can further reduce the generationof debris, stably supply the high temperature plasma raw material (tin)to the plasma generating region, and ensure stable light emission ofEUV. In particular, the object of the present invention is to provide adevice for supplying the high temperature plasma raw material that canbe used with the LPP method.

Solution to the Problems

The inventors made studies and investigations to overcome theabove-described problems, and arrived at an idea of disposing acover-like structure around a rotating element to prevent the produceddebris from scattering in the plasma generating space such that thescattered liquid plasma raw material is trapped on the inner surface ofthe cover and guided to a first reserving vessel below the cover-likestructure. The inventors also arrived at an idea of circulating theliquid material, which is received in the first reserving vessel, toutilize it again for the EUV generation. The inventors also arrived atan idea of attaching to the rotating element a mechanism for reforming arotating element surface to improve the contact property, i.e.,wettability, between the rotating element and the liquid plasma rawmaterial for the purpose of reducing the scattering of the debris.

Specifically, the present invention provides the extreme ultravioletlight source devices in the following configurations.

(1) According to one aspect of the present invention, there is providedan extreme ultraviolet light source device that includes a disc-likerotating element (rotor), a rotation unit for causing the rotatingelement to rotate about a rotation center shaft, which is perpendicularto a flat portion of the rotating element, a cover-like structure(member) for surrounding (receiving) the rotating element with a gap, afirst reserving vessel disposed in the cover-like structure forreserving (storing) a liquid high temperature plasma raw material, withpart of the rotating element being immersed in the high temperatureplasma raw material reserved in the first reserving vessel, a rawmaterial supplying mechanism for applying the liquid high temperatureplasma raw material onto at least part of a surface of the rotatingelement upon a rotating movement of the rotating element, and an energybeam providing device for irradiating the high temperature plasma rawmaterial with an energy beam. The cover-like structure of the rawmaterial supplying mechanism has an opening in (at) a certain part ofthe cover-like structure. The energy beam is directed to that surface ofthe rotating element, on which the high temperature plasma raw materialis applied, through the opening of the cover-like structure. Extremeultraviolet light generated upon irradiation of the energy beam isreleased from the opening of the cover-like structure. The cover-likestructure has a scattering preventing member disposed to oppose adirection of a centrifugal force acting on the rotating element, whichis caused to rotate by the rotation unit, and cover the rotatingelement.

(2) In another embodiment of the present invention, the gap between therotating element and the cover-like structure may be decided (set) suchthat the liquid high temperature plasma raw material applied onto therotating element has a predetermined film thickness.

(3) In still another embodiment of the present invention, a filmthickness controlling mechanism may be provided in the cover-likestructure. The film thickness controlling mechanism may face thatsurface of the rotating element, on which the high temperature plasmaraw material is applied, with a predetermined clearance. The clearancemay be decided (set) such that the liquid high temperature plasma rawmaterial applied on the rotating element has a predetermined filmthickness. The film thickness controlling mechanism may be located at aposition that enables the adjustment of the film thickness of the hightemperature plasma raw material in that region of the rotating elementwhich is irradiated with the energy beam.

(4) In yet another embodiment of the present invention, a film thicknesscontrolling (regulating) mechanism, which includes a structure having achannel-like recess, may be provided in the cover-like structure. Therecess of the structure may face the rotating element. The recess mayhave an opening, and two sides of the structure along opposite edges ofthe opening of the recess may extend in the circumferential direction ofthe rotating element. A clearance between the rotating element and abottom of the recess of the structure, which faces the rotating element,may be set (decided) such that the liquid high temperature plasma rawmaterial applied on the rotating element has a predetermined filmthickness. The film thickness controlling mechanism having theabove-described structure may be located at a position that can adjustthe film thickness of the high temperature plasma raw material in thatregion of the rotating element which is irradiated with the energy beam.The structure may be biased by a resilient member (elastic body) in adirection against the surface of the rotating element such that the twosides of the structure along the opposite edges of the recess maycontact the surface of the rotating element.

(5) In another embodiment of the present invention, the energy beam maybe directed to one of the two surfaces of the disc-like rotatingelement, which are perpendicular to the rotation center shaft, from adirection of the normal line to the surface of the disc-like rotatingelement or from a direction crossing the direction of the normal line tothe surface of the disc-like rotating element. An optical axis of theextreme ultraviolet light may be decided on the basis of a positionwhere the high temperature plasma, which emits the extreme ultravioletlight, is generated and a position where an extreme ultraviolet lightcondensing mirror is mounted, or on the basis of the position where thehigh temperature plasma is generated and an optical system used to testa mask. The optical axis of the extreme ultraviolet light may be setsuch that the energy beam directed to the rotating element may notcoincide with a direction of the energy beam reflected by the rotatingelement.

(6) In another embodiment of the present invention, the optical axis ofthe extreme ultraviolet light may coincide with the direction of thenormal line to a plane perpendicular to the rotation center shaft of thedisc-shaped rotating element, onto which the high temperature plasma rawmaterial is applied.

(7) In another embodiment of the present invention, the extremeultraviolet light source device may further include a cooling unit forcooling the liquid high temperature plasma raw material such that theliquid high temperature plasma raw material applied on the rotatingelement is transformed to a solid near a region where the rotatingelement is irradiated with the energy beam passing through the openingof the cover-like structure.

(8) In another embodiment of the present invention, the rotation centershaft of the rotating element may not be perpendicular to the directionof the normal line to the liquid surface of the liquid high temperatureplasma raw material reserved in the first reserving vessel, but maycross the direction of the normal line to the liquid surface of theliquid high temperature plasma raw material reserved in the firstreserving vessel.

(9) In another embodiment of the present invention, a groove, a recessor a through hole may be formed in at least one of two faces of thedisc-like rotating element which is irradiated with the energy beam. Thetwo faces of the rotating element are perpendicular to the rotationcenter shaft of the rotating element.

(10) In another embodiment of the present invention, a surface texturingprocess may be applied on at least one of two faces of the disc-likerotating element in a region irradiated with the energy beam. The twofaces of the rotating element are perpendicular to the rotation centershaft of the rotating element.

(11) In another embodiment of the present invention, a mechanism forapplying a surface reforming process with plasma may be provided. Thismechanism applies the surface reforming process to at least one of twofaces of the disc-like rotating element in a region irradiated with theenergy beam. The two faces of the rotating element are perpendicular tothe rotation center shaft of the rotating element.

(12) In another embodiment of the present invention, an electrode may beprovided such that the electrode faces at least one of two faces of thedisc-like rotating element in a region irradiated with the energy beam.The two faces of the rotating element are perpendicular to the rotationcenter shaft of the rotating element. Also, a power source device may beprovided for applying a voltage across the electrode and the rotatingelement.

(13) In another embodiment of the present invention, the extremeultraviolet light source device may further include a liquid rawmaterial circulating device. The liquid raw material circulating devicemay include a second reserving vessel configured to reserve (store) thehigh temperature plasma raw material, a raw material inflow conduitconnected between the second reserving vessel and the first reservingvessel and configured to allow the high temperature plasma raw materialto flow in the first reserving vessel from the second reserving vessel,a raw material outflow conduit connected between the second reservingvessel and the first reserving vessel and configured to allow the hightemperature plasma raw material to flow in the second reserving vesselfrom the first reserving vessel, and a raw material drive unitconfigured to convey the high temperature plasma raw material to thefirst reserving vessel from the second reserving vessel.

(14) In another embodiment of the present invention, the secondreserving vessel of the liquid raw material circulating device may belocated such that the liquid surface of the liquid high temperatureplasma raw material reserved in the second reserving vessel is lowerthan the liquid surface of the liquid high temperature plasma rawmaterial reserved in the first reserving vessel when viewed in thegravity direction.

(15) In another embodiment of the present invention, the energy beamdirected to that surface of the rotating element onto which the hightemperature plasma raw material is applied may be a laser beam.

(16) In another embodiment of the present invention, the energy beamdirected to that surface of the rotating element onto which the hightemperature plasma raw material is applied may include two laser beams.

Advantageous Effects of the Invention

The LPP type extreme ultraviolet light source device of the presentinvention has the following advantages.

(1) The raw material supplying mechanism of the LPP type extremeultraviolet light source device of the present invention applies theliquid high temperature plasma raw material on the rotating element inthe form of thin film, and the rotating element except for the region tobe irradiated with the energy beam is surrounded by the cover-likestructure. Thus, it is possible to suppress the scattering of the liquidhigh temperature plasma raw material from the rotating element.

(2) When the opening is formed in a certain part of the cover-likestructure to expose at least the planar surface of the rotating element(i.e., the surface perpendicular to the rotation shaft of the rotatingelement, or the side face of the rotating element), on which the hightemperature plasma raw material is applied, then the debris generatedupon irradiation of the energy beam is not released out of thecover-like structure unless the debris passes through the opening.Therefore, it is possible to reduce an amount of the debris released tothe high temperature plasma generating space that emits the EUV light,as compared to conventional configurations.

(3) When part of the rotating element is immersed in the hightemperature plasma raw material, which is reserved in the firstreserving vessel, and the liquid high temperature plasma raw material isapplied onto at least a certain part of the surface of the rotatingelement upon a rotating movement of the rotating element, then the hightemperature plasma raw material is stably supplemented to that region ofthe rotating element which is irradiated with the energy beam while thehigh temperature plasma raw material being consumed upon the irradiationof the energy beam. Thus, it is possible to obtain stable EUV radiation(stable EUV light emission).

(4) When the gap between the rotating element and the cover-likestructure is decided such that the liquid high temperature plasma rawmaterial applied onto the rotating element has a predetermined filmthickness, then the liquid high temperature plasma raw material appliedon part of the side face of the rotating element can have a desired filmthickness that is suitable for EUV radiation to be obtained uponirradiation of the energy beam.

(5) When the film thickness controlling mechanism is provided such thatthe liquid high temperature plasma raw material applied on the rotatingelement has a predetermined film thickness, then the liquid hightemperature plasma raw material applied on part of the side face of therotating element can have a desired film thickness that is suitable forEUV radiation to be obtained upon irradiation of the energy beam.

(6) In particular, when the film thickness controlling mechanismincludes a channel-like structure having a recess, the recess of thechannel-like structure faces the rotating element, and the channel-likestructure is biased by the elastic body such that the channel-likestructure is forced to contact the rotating element, then the filmthickness controlling mechanism follows the movement of the rotatingelement even if the rotating element shakes and moves while the rotatingelement is rotating, and it is ensured that the liquid high temperatureplasma raw material applied on part of the side face of the rotatingelement can have a desired film thickness that is suitable for EUVradiation to be obtained upon irradiation of the energy beam.

(7) When one of the two planar surfaces of the rotating element, onwhich the high temperature plasma raw material is applied, is irradiatedwith the energy beam, and the optical axis of the extreme ultravioletlight does not coincide with the proceeding direction of the energy beamreflected by the rotating element, then there is an advantage that it ispossible to prevent undesired direct light of the energy beam (e.g.,laser beam) from arriving at the downstream exposure device (scanner),and only allow necessary EUV radiation (light) to arrive at the scanner.If the extreme ultraviolet light source is used as a light source forthe mask testing, it is possible to prevent the undesired direct lightof the energy beam (e.g., laser beam) from arriving at the downstreamoptical system for the mask testing, and only allow the necessary EUVradiation to arrive at the optical system for the mask testing.

(8) When the extreme ultraviolet light source device further includes acooling unit for cooling the liquid high temperature plasma raw materialsuch that the liquid high temperature plasma raw material applied on therotating element is transformed to a solid in and/or near a region wherethe rotating element is irradiated with the energy beam passing throughthe opening of the cover-like structure, then it is possible to furtherreduce the scattering of the high temperature plasma raw material uponirradiation of the energy beam, and suppress the generation of thedebris.

(9) When the rotation center shaft of the rotating element is notperpendicular to the direction of the normal line to the liquid surfaceof the liquid high temperature plasma raw material reserved in the firstreserving vessel but crosses the direction of the normal line to theliquid surface of the liquid high temperature plasma raw materialreserved in the first reserving vessel, then the liquid high temperatureplasma raw material is applied to part of the surface of the rotatingelement in a more reliable manner, and the lifting up of the liquid hightemperature plasma raw material by the rotation of the rotating elementis further facilitated.

(10) The high temperature plasma raw material is applied onto the twofaces (planar surfaces) of the rotating element. When the groove isformed in at least that face out of two faces of the disc-like rotatingelement which is irradiated with the energy beam, then the liquid hightemperature plasma raw material is applied and retained in the groove.Thus, it is possible to convey the liquid high temperature plasma rawmaterial to a region to be irradiated with the energy beam in a reliablemanner upon the rotation of the rotating element.

(11) The high temperature plasma raw material is applied onto the twofaces (planar surfaces) of the rotating element. When the surfacetexturing process or a surface reforming (modification) treatment withplasma is applied on at least one of the two faces of the rotatingelement in a region irradiated with the energy beam, then thewettability of the rotating element, which is made from a high meltingpoint metal such as molybdenum, to the liquid high temperature plasmaraw material such as tin is improved. Thus, the surface of the rotatingelement has a better contact with the liquid high temperature plasma rawmaterial, and the liquid raw material is applied onto the rotatingelement in a more reliable manner.

(12) When the extreme ultraviolet light source device further includesthe liquid raw material circulating device, and the liquid raw materialcirculating device has the second reserving vessel configured to reservethe high temperature plasma raw material, the raw material inflowconduit, the raw material outflow conduit, and the raw material driveunit configured to convey the high temperature plasma raw material tothe first reserving vessel from the second reserving vessel, then thehigh temperature plasma raw material is circulated between the firstreserving vessel and the second reserving vessel, which has a largercapacity than the first reserving vessel, and the high temperatureplasma raw material to be stored in the first reserving vessel can havea constant (predetermined) volume for a long time. As a result, it ispossible to stably perform the EUV radiation for a long time. If thehigh temperature plasma raw material is circulated for reuse, then it ispossible to reduce the consumption of the liquid high temperature plasmaraw material.

(13) The high temperature plasma raw material in the first reservingvessel is heated by the rotating element as the rotating element isheated upon irradiation of the energy beam. Then, the wettability of therotating element to the high temperature plasma raw material may change,and the contact condition of the high temperature plasma raw materialwith the rotating element may also change. As a result, the output ofthe EUV radiation may change. However, when the high temperature plasmaraw material is circulated between the first reserving vessel and thesecond reserving vessel, which has a larger capacity than the firstreserving vessel, the temperature of the high temperature plasma rawmaterial does not change very much. Therefore, it is possible to provideEUV radiation having a stable output.

(14) When the second reserving vessel of the liquid raw materialcirculating device is located such that the liquid surface of the liquidhigh temperature plasma raw material reserved in the second reservingvessel is lower than the liquid surface of the liquid high temperatureplasma raw material reserved in the first reserving vessel when viewedin the gravity direction, then the liquid high temperature plasma rawmaterial does not flow in the first reserving vessel from the secondreserving vessel even if the liquid raw material circulating devicefails. Accordingly, a problem that the high temperature plasma rawmaterial flows into the chamber through the opening of the firstreserving vessel does not occur.

(15) In addition, when the above-described configuration is employed,the liquid high temperature plasma raw material itself serves as athermal medium to receive a radiant heat from the plasma generated uponirradiation of the laser beam. Therefore, an advantage arises, i.e., thehigh temperature plasma raw material cools the rotating element and thesurrounding atmosphere.

(16) It should be noted that when the above-described configuration isemployed, a usable solid angle becomes an approximately half (2πsr), ascompared to the conventional droplet method and a method of irradiatingthe radially outer surface of the rotating element with the energy beam.However, this is still adequately practical, when an advantage ofreducing the debris to be generated is taken into account.

The above-described objects, aspects and advantages of the presentinvention and other objects, aspects and advantages of the presentinvention will be understood by a skilled person from the following“mode for carrying out the invention” (detailed description of thepresent invention) when the accompanying drawings and the claims arereferred to.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates a structure of an LPP type extreme ultraviolet (EUV)light source device according to an embodiment of the present invention.

FIG. 1B illustrates the extreme ultraviolet light source device of FIG.1A when viewed in the direction of the arrow Y.

FIG. 2A is a conceptual view of a film thickness controlling device, andshows an enlarged cross-sectional view taken along the line A-A in FIG.1A.

FIG. 2B shows the film thickness controlling device of FIG. 2A whenviewed in the direction of the arrow B.

FIG. 3A is another conceptual view of the film thickness controllingdevice, and shows an enlarged cross-sectional view taken along the lineA-A in FIG. 1A.

FIG. 3B is a perspective view of a structure having a recess that isshown in FIG. 3A.

FIG. 3C is a conceptual view showing another structure of the filmthickness controlling device, and shows an enlarged cross-sectional viewtaken along the line C-C in FIG. 1A without a film thickness controllingmechanism 5.

FIG. 4 is a view useful to describe relation between an optical axis ofthe EUV light and a proceeding direction of an energy beam, when viewedin the direction of the arrow Z in FIG. 1A.

FIG. 5 is a view useful to describe recovery of flying particles of thehigh temperature plasma raw material in a first reserving vessel by ascattering prevention structure.

FIG. 6A is a view useful to describe an exemplary cover-like structurethat has an opening at a position facing a side face (flat surface) of arotating element.

FIG. 6B is a cross-sectional view of the cover-like structure of FIG.6A, taken along the line D-D.

FIG. 7 illustrates a configuration of the rotating element that has acenter rotating shaft inclined relative to the direction of a normalline to the liquid surface of the liquid high temperature plasma rawmaterial.

FIG. 8 illustrates a configuration that reforms a surface of therotating element with the discharge plasma.

FIG. 9A illustrates an exemplary rotating element that has a groove in asurface of the rotating element.

FIG. 9B is a cross-sectional view of the rotating element of FIG. 9A,taken along the line E-E, together with the cover-like structure.

FIG. 10 is similar to FIG. 9A, and shows an exemplary rotating elementthat has a groove in a surface of the rotating element.

FIG. 11 shows a structure of a conventional LDP type extreme ultraviolet(EUV) light source device.

FIG. 12 shows a structure of a conventional LPP type extreme ultraviolet(EUV) light source device.

MODE FOR CARRYING OUT THE INVENTION

FIGS. 1A and 1B show major components of an LPP type extreme ultravioletlight source device (hereinafter, referred to as “EUV light sourcedevice”) according to an embodiment of the present invention. Thoseportions which are indicated by the broken line are components disposedinside a cover-like structure, and cannot be seen from outside. Itshould also be noted that FIGS. 1A and 1B are schematic views which areprepared for the sake of description. Actual size relation between thecomponents shown in FIGS. 1A and 1B is not exactly the same as thatshown in FIGS. 1A and 1B.

General Description of Raw Material Supplying Mechanism

Structures and operations of the respective parts of a raw materialsupplying mechanism of an EUV light source device of this embodimentwill now be described below.

FIGS. 1A and 1B show the raw material supplying mechanism in the LPPtype EUV light source device according to the embodiment of the presentinvention. FIG. 1A illustrates a rotating element 1 disposed in the rawmaterial supplying mechanism, when viewed in the direction of a rotationcenter shaft 3 of the rotating element 1, together with a liquid rawmaterial circulating device 7. FIG. 1B illustrates the rotating element1 and a motor 13 for causing the rotating element to rotate when viewedin a direction perpendicular to the rotation center shaft 3.

As shown in FIG. 1B, the raw material supplying mechanism is disposedinside a chamber 20, i.e., a plasma generating container. The interiorof the chamber 20 is maintained in a vacuum condition.

Major components of the raw material supplying mechanism are therotating element 1, a cover-like structure 2, a first reserving vessel4, and the liquid raw material circulating device 7.

The rotating element 1 rotates about the rotation center shaft 3, andpart of the rotating element is immersed in the first reserving vessel 4(inside the cover-like structure 2), which reserves a liquid hightemperature plasma raw material 23. The rotating element 1 is made froma metal having a high melting point such as tungsten, molybdenum ortantalum.

Referring now to FIG. 1B, the rotation center shaft 3 of the rotatingelement 1 is coupled to a rotation shaft 13 a of a motor 13 via acoupling 16. Thus, the rotating element 1 rotates as the rotation shaft13 a of the motor 13 rotates. The rotation center shaft 3 or therotation shaft 13 a of the motor 13 extends into the chamber 20, forexample, via a mechanical seal 14. The mechanical seal 14 allows therotation center shaft 3 or the rotation shaft 13 a of the motor 13 torotate while maintaining the reduced pressure atmosphere inside thechamber 20. FIG. 1B shows an example when the rotation shaft 13 a of themotor 13 extends into the chamber 20 via the mechanical seal 14.

The rotating element 1 is surrounded by or received in the cover-likestructure 2 except for a region to be irradiated with an energy beam 6′from an energy beam supplying device 6. In other words, the cover-likestructure 2 has an opening 15 that corresponds to a passing region ofthe energy beam 6′.

The cover-like structure 2 is configured such that a lower part of thecover-like structure function as a first reserving vessel 4 forreserving the liquid high temperature plasma raw material 23.Specifically, the liquid high temperature plasma raw material 23 isintroduced into the cover-like structure 2. It should be noted that thecover-like structure 2 may not function as the first reserving vessel 4,i.e., a separate first reserving vessel 4 may be disposed inside thecover-like structure 2.

As the rotating element 1 rotates about the rotation center shaft 3, theliquid high temperature plasma raw material 23 is pulled up and conveyedfrom the first reserving vessel 4 along the surface of the rotatingelement because of the wettability between the surface of the rotatingelement 1 and the liquid high temperature plasma raw material 23. Thereis a gap between the cover-like structure 2 and the rotating element 1such that the rotating element 1 can rotate without interference.

Film Thickness Controlling Mechanism

The liquid high temperature plasma raw material 23 applied onto part ofthe surface of the rotating element 1 in the form of thin film in theabove-described manner is guided to a film thickness controllingmechanism 5 disposed in the cover-like structure 2 upon rotation of therotating element 1.

The film thickness controlling mechanism 5 is located to have apredetermined clearance between the rotating element 1 and the filmthickness controlling mechanism 5. The film thickness controllingmechanism 5 is located at a position that can adjust the film thicknessof the high temperature plasma raw material 23 in that region of therotating element 1 which is to be irradiated with the energy beam 6′.

This predetermined clearance corresponds to the desired film thicknessof the high temperature plasma raw material 23 applied onto the rotatingelement 1. Therefore, the liquid high temperature plasma raw material 23applied onto the rotating element 1 is controlled such that the filmthickness of the high temperature plasma raw material 23 on the rotatingelement 1 has the desired film thickness as the high temperature plasmaraw material 23 passes through the film thickness controlling mechanism5.

The liquid high temperature plasma raw material 23 having the controlledfilm thickness on the rotating element 1 is conveyed to the opening 15of the cover-like structure 2 (i.e., the region to be irradiated withthe energy beam 6′) upon the rotation of the rotating element 1. Inother words, the rotating element 1 rotates such that the liquid hightemperature plasma raw material 23 on the rotating element 1 passesthrough the film thickness controlling mechanism 5 and then the hightemperature plasma raw material 23 is conveyed to the region to beirradiated with the energy beam 6′, as indicated by the arrow in FIG.1A.

One example of the film thickness controlling mechanism 5 will bedescribed with reference to FIGS. 2A, 2B and FIGS. 3A to 3C. The LPPtype extreme ultraviolet (EUV) light source device in this embodimentdoes not utilize the liquid high temperature plasma raw material 23applied on an outer edge face (circumferential portion) in a radialdirection of the rotating element 1 for EUV radiation as disclosed inPatent Literature 1 (Japanese Patent Application Laid-Open PublicationNo. 2007-505460) or Patent Literature 3 (PCT International PublicationNo. 2009/077943). Rather, the LPP type extreme ultraviolet light sourcedevice in this embodiment utilizes the liquid high temperature plasmaraw material 23 applied on a side face of the rotating element 1 (planeperpendicular to the rotation center shaft of the rotating element 1,which may be referred to as “planar surface” hereinafter).

The film thickness controlling device 5 is configured to form (shape)the liquid high temperature plasma raw material 23 in the thin film,which is applied onto part of the side face of the rotating element 1,such that the liquid high temperature plasma raw material has apredetermined film thickness that is suitable for EUV radiation.

FIG. 2A shows an exemplary configuration of the film thicknesscontrolling mechanism. FIG. 2A is a cross-sectional view taken along theline A-A in FIG. 1A. The structure that constitutes the film thicknesscontrolling mechanism 5 shown in FIG. 2A is a block-like structure 5 amounted on an inner wall of the cover-like structure 2. The block-likestructure 5 a serves as a scraper to scrape part of the liquid hightemperature plasma raw material 23 applied on part of the side face(planar surface) of the rotating element 1.

The clearance between the rotating element 1 and that surface of thestructure 5 a of the film thickness controlling mechanism 5, which facesthe rotating element 1, is set to K. The clearance K is decided suchthat the liquid high temperature plasma raw material 23 applied on partof the side face of the rotating element 1 has a predetermined (desired)film thickness that is suitable for EUV radiation. In other words, theclearance K is equal to the above-mentioned predetermined filmthickness.

The location of the film thickness controlling mechanism 5 is decidedsuch that the film thickness control can be carried out in a region thatencompasses that position on the rotating element 1 which is irradiatedwith the energy beam 6′.

The thickness of the film thickness controlling mechanism 5 itself maybe greater than the thickness of the cover-shaped structure 2. In suchconfiguration, the film thickness controlling mechanism 5 may protrudefrom the cover-shaped structure 2, as indicated by the broken line inFIG. 2A.

FIG. 2B shows another configuration of the film thickness controllingmechanism 5 that includes a plate-like structure 5 b, instead of theblock-like structure. FIG. 2B is a drawing when viewed in the directionof the arrow B in FIG. 2A.

Specifically, the film thickness controlling mechanism 5 includes theplate-like structure 5 b and is disposed such that the plate-likestructure 5 b inclines relative to the surface of the rotating element1. This configuration can also achieve the same function as theblock-shaped film thickness controlling mechanism 5. It should be notedthat that end of the plate-shaped structure 5 b which faces the surfaceof the rotating element 1 may have a knife edge shape, if necessary.

FIG. 3A shows another configuration of the film thickness controllingmechanism 5. FIG. 3A is a cross-sectional view taken along the line A-Ain FIG. 1A. The film thickness controlling mechanism 5 shown in FIG. 3Aincludes a structure 5 c having a channel-like recess. FIG. 3B is aperspective view of the structure 5 c having the channel-like recess(concave portion) when looked at from the rotating element 1. Asillustrated in FIG. 3B, the structure 5 c has a channel-like(trough-like) concave portion or recess 5 d. The recess 5 d has anopening 5 e, and both sides of the opening 5 e are planar portions.

The structure 5 c is placed on the rotating element such that thechannel-like concave portion 5 d faces the rotating element 1. Bothsides of the structure 5 c along opposite edges of the opening 5 e ofthe concave portion 5 d contact the surface of the rotating element 1,and the sides 5 f along the opposite edges of the opening of the concaveportion 5 d extend along the circumferential direction of the rotatingelement 1 (i.e., extend perpendicularly to the radial direction of therotating element 1). The structure 5 c serves as a scraper to scrapepart of the liquid high temperature plasma raw material 23, which isapplied on part of the side face (planar surface) of the rotatingelement 1.

The clearance between the rotating element 1 and that inner surface ofthe structure 5 c of the film thickness controlling mechanism 5 whichfaces the rotating element 1 (i.e., bottom of the channel-shaped recess5 d) is set to K. The clearance K is decided such that the liquid hightemperature plasma raw material 23 applied on part of the side face ofthe rotating element 1 has a predetermined thickness that is suitablefor EUV radiation. Thus, the clearance K is equal to the predeterminedfilm thickness.

The structure 5 c is biased by an elastic body (resilient member) 5 g ina direction against the surface of the rotating element 1 (direction ofthe arrow G). Thus, even if the rotating element 1 shakes and moves inthe direction of the arrow H while the rotating element 1 is rotating,the film thickness controlling mechanism 5 follows the movement of therotating element 1, and works such that the film thickness of the liquidhigh temperature plasma raw material 23 applied on part of the side faceof the rotating element 1 becomes equal to the clearance K.

FIG. 3C depicts another configuration of the film thickness controllingmechanism. The film thickness controlling mechanism 5 shown in FIG. 3Cis the cover-shaped structure 2 which additionally possesses thefunction of the film thickness controlling mechanism 5. FIG. 3C is across-sectional view taken along the line C-C in FIG. 1A, without thefilm thickness controlling mechanism 5.

Thus, the clearance between the side face of the rotating element 1 andthat surface of the cover-like structure 2 which faces the side face(planar surface) of the rotating element 1 is set to K. The clearance Kis decided such that the liquid high temperature plasma raw material 23applied on part of the side face of the rotating element 1 has apredetermined film thickness that is suitable for EUV radiation. Thus,the clearance K is equal to the predetermined film thickness.

In any of the film thickness controlling mechanisms shown in FIGS. 2A,2B, 3A, 3B and 3C, the liquid high temperature plasma raw material 23applied on part of the side face (planar surface) of the rotatingelement 1 is scraped by the film thickness controlling mechanism 5 whenthe high temperature plasma raw material 23 passes through the filmthickness controlling mechanism 5. As a result, the liquid hightemperature plasma raw material 23 applied on part of the side face ofthe rotating element 1 is controlled to have the desired film thicknessthat is suitable for EUV radiation as the high temperature plasma rawmaterial passes through the film thickness controlling mechanism 5.

Energy Beam

Referring back to FIGS. 1A and 1B, the cover-like structure 2 has theopening 15 that corresponds to the passage region for the energy beam6′, as described above. The liquid light source plasma raw materialapplied on the side face (planar surface) of the rotating element 1,which is exposed by the opening 15 of the cover-like structure 2, isirradiated with the energy beam 6′ from the energy beam providing device6. As a result, the plasma raw material is vaporized and generates theEUV radiation.

In recent years, a prepulse process is employed as disclosed in PatentLiterature 5 (Japanese Patent Application Laid-Open Publication No.2005-17274) and Patent Literature 6 (Japanese Patent ApplicationLaid-Open Publication No. 2010-514214). The prepulse process irradiatesa single raw material in an LPP type EUV light source device with alaser beam for a plurality of times. This approach firstly irradiatesthe high temperature plasma raw material 23 with a first energy beam(prepulse such as a YAG laser beam) to generate a weak plasma, therebyreducing the density of the high temperature plasma raw material 23.Then, this approach irradiates the weak plasma with a second energy beam(main pulse such as a CO₂ laser beam).

By reducing the density of the raw material with the prepulse, theabsorption of the main pulse (CO₂ laser beam) into the raw material isimproved, and the EUV radiation intensity is enhanced. Also, the plasmahas a relatively small density, and the recapturing (reabsorption) ofthe EUV radiation decreases. Thus, the EUV generation efficiency isimproved, and the debris generation is decreased.

As such, it is preferred that the energy beam directed to the liquidlight source plasma raw material includes at least two laser beams, asdescribed above. A device for emitting the energy beam (for irradiatingthe plasma raw material with the energy beam) may be, for example, a CO₂gas laser source, a solid laser source such as a YAG laser source, or anexcimer laser source such as an ArF laser, a KrF laser or a XeCl laser.

In this embodiment, the laser beam is used as the energy beam to bedirected to the high temperature plasma raw material. It should benoted, however, that an ion beam or an electron beam may be directed,instead of the laser beam, to the liquid high temperature plasma rawmaterial (tin) applied on the side face (planar surface) of the rotatingelement.

The energy beam (e.g., laser beam) is directed in a direction toward theside face (planar surface) of the rotating element. The high temperatureplasma is generated at that position on one side face (planar surface)of the rotating element, which is irradiated with the laser beam. Theplasma radiates the EUV light in the direction of a solid angle of 2πsr.

FIG. 4 is a view useful to describe the relation between the opticalaxis of the EUV light and the proceeding direction of the energy beam.The same reference numerals are assigned to the same components andelements in FIGS. 1A, 1B and 4. The configuration shown in FIG. 4includes the configuration shown in FIGS. 1A and 1B and further includesa foil trap 21 for capturing the debris generated from the hightemperature plasma, an EUV light condensing mirror 22 for condensing theradiated EUV light to an intermediate condensing spot IF, and anexposure device 30.

In this embodiment, the EUV light condensing mirror 22 (oblique incidentmirror) is disposed such that the optical axis T of the EUV lightextends in the direction of the normal line to the side face of therotating element 1, as shown in FIG. 4. Then, the center of the foiltrap 21, the intermediate condensing point (IF) of the EUV light, andthe exposure device 30 are aligned (arranged) on the optical axis T ofthe EUV light that extends in the direction of the normal line to theside face of the rotating element 1.

In such arrangement, the laser beam (energy beam 6′) is directed to thesurface of the rotating element 1 from (in) an oblique direction. Inother words, the laser beam emitting direction is decided such that thereflecting direction of the laser beam by the rotating element 1 doesnot coincide with the optical axis T of the EUV light.

If the EUV light condensing mirror 22 is located as indicated by thebroken line in FIG. 4 such that the reflecting direction of the laserbeam by the rotating element 1 coincides with the optical axis T of theEUV light, then the laser beam (energy beam 6′) that does not contributeto the generation of the high temperature plasma (i.e., EUV radiation)is introduced to the downstream exposure device 30 (scanner) in thechamber 20. This would raise a problem such as temperature elevation ofthe exposure device 30.

For example, when a conventional droplet type raw material supplyingmethod shown in FIG. 12 is used, the energy beam is directed to theoptical axis of the EUV radiation from behind the center portion of theEUV reflection mirror. Thus, similar to the above-describedconfiguration, the energy beam that does not contribute to the EUVradiation is introduced to the downstream exposure device (scanner). Incase of the light source for the mask testing, the energy beam isintroduced to a downstream optical system for the mask testing.

As described above, the above-mentioned problem will be avoided if thelaser emitting direction is decided such that the reflecting directionof the laser beam by the rotating element does not coincide with theoptical axis of the EUV light.

In the above-described example, the EUV light source device is used asthe light source for exposure. The optical axis of the EUV light isdecided by the generating position of the high temperature plasma thatemits the EUV light and the mounting position of the EUV lightcondensing mirror. In case of the light source for the mask testing, onthe other hand, the optical axis of the EUV light is decided by theoptical system for the mask testing and the generating position of thehigh temperature plasma that emits the EUV light, as disclosed in PatentLiterature 7 (Japanese Patent Application No. 2012-235043).

It should be noted that although the optical axis of the EUV lightextends in the direction of the normal line to the side face of therotating element 1 in the above-described example, the present inventionis not limited in this regard. Specifically, the optical axis T of theEUV light may not extend in the direction of the normal line to the sideface of the rotating element 1. In either configuration, theabove-described problem is overcome by arranging the laser beam emittingdirection such that the reflecting direction of the laser beam by (from)the rotating element does not coincide with the optical axis of the EUVlight.

Suppressing Scattering of High Temperature Plasma Raw Material (1)

Referring back to FIGS. 1A and 1B, the cover-shaped structure 2 thatsurrounds the rotating element 1 has the opening 15 that corresponds tothe passage region of the energy beam 6′, as described above. Thus, asthe rotating element 1 having the high temperature plasma raw material23 applied thereon rotates, part of the applied high temperature plasmaraw material 23 may scatter from the opening 15 into the chamber 20. Inorder to suppress such scattering (splashing) of particles of the hightemperature plasma raw material 23, a scattering preventing structure ormember 9 is provided at the opening 15 of the rotating element 1.

The scattering preventing member 9 is a plate-like member and disposedat the opening 15 of the cover-like structure 2 such that the scatteringpreventing member 9 faces a circumferential face or edge (circularportion or a bending face) of the disc-like rotating element 1. Thescattering preventing member 9 covers the rotating element and isdirected opposite the direction of a centrifugal force acting on therotating element, which is caused to rotate by the rotation unit. Thatface of the scattering preventing member 9 which faces thecircumferential face of the rotating element 1 (hereinafter,occasionally referred to as “facing surface”) is, for example, a bendingsurface.

As shown in FIG. 5, the particles 10 of the high temperature plasma rawmaterial 23 scattering or spreading in a direction of the centrifugalforce upon the rotation of the rotating body 1 collide with the facingsurface of the scattering preventing member 9. The spreading particles10 that collide with the facing surface are reflected by the facingsurface and/or adhere to the facing surface. Most of the reflectedparticles 10 moves into the cover-shaped structure 2, and returns to thefirst reserving vessel 4. Some of the particles 10 adhering onto thefacing surface move downward along the facing surface in the gravitydirection, and return to the first reserving vessel 4.

In this manner, the scattering preventing member 9 catches the spreadingparticles 10 flying from the rotating body 1, and causes part of theparticles 10 to return to the first reserving vessel 4. Thus, theprovision of the scattering preventing member 9 at the opening 15 of thecover-shaped structure 2 can suppress the spreading of part of the hightemperature plasma raw material 23 into the chamber 20 from the opening15. It should be noted that the scattering preventing member 9 does nothinder the travelling (proceeding) of the energy beam 6′ that isdirected to the side face of the rotating body 1 because the scatteringpreventing member 9 faces the circumferential portion (bending face) ofthe disc-shaped rotating element 1.

Suppressing Scattering of High Temperature Plasma Raw Material (2)

FIGS. 6A and 6B show another embodiment of the structure for preventingthe scattering. FIG. 6A illustrates the side face (planar surface) ofthe cover-like structure 2 having the scattering prevention structure.FIG. 6B is a cross-sectional view taken along the line D-D in FIG. 6A.

In the configuration shown in FIGS. 1A and 1B, the opening 15 formed inthe cover-like structure 2 that surrounds the rotating element 1 exposespart of the two side faces (two planar surfaces) of the rotating element1 and part of the circumferential portion (bending surface). Thescattering prevention structure 9 is disposed at the opening 15 of thecover-like structure 2 such that the scattering prevention structure 9faces the circumferential face (bending surface) of the rotating element1.

In the configuration shown in FIGS. 6A and 6B, an opening 11 is formedin the cover-like structure 2 that surrounds the rotating element 1 suchthat the opening 11 is positioned to expose part of one of the two sidefaces (planar surface) of the rotating element 1. Part of the cover-likestructure 2 serves as the scattering preventing member 9 shown in FIG.1A. That part of the side face of the rotating element 1, which isexposed by the opening 11, is irradiated with the energy beam 6′ andthis part is a region where the EUV light is generated (EUV lightemission takes place) as the high temperature plasma raw material 23 isirradiated with the energy beam 6′. Thus, the opening 11 is provided notto block or obstruct the travelling of the energy beam 6′ and thegenerated EUV light.

Having such configuration, the cover-like structure 2 surrounds theentire circumferential portion (bending surface) of the rotating element1. Thus, the flying particles of the liquid high temperature plasma rawmaterial 23 that spreads (scatters) from the rotating element 1 in thedirection of the centrifugal force is completely captured by thecover-like structure 2, and part of the captured particles return to thefirst reserving vessel 4. The particles scattering from the rotatingelement 1 can only proceed into the chamber 20 through the opening 11.Thus, the configuration of this embodiment imparts the function of thescattering preventing member 9 of FIG. 1A to the cover-like structure 2.The exposed portion of the rotating element 1 is limited to the region,through which the energy beam 6′ proceeds. Because the exposed portionof the rotating element 1 is smaller than the exposed portion shown inFIG. 1A, it is possible to significantly reduce the spreading particlesfrom the rotating element 1 and the particles proceeding into thechamber 20, as compared to the configuration shown in FIG. 1A.

The scattering preventing member 9 shown in FIG. 1A collects (recovers)the high temperature plasma raw material 23 scattering in the directionof the centrifugal force of the rotating element 1, but cannot suppressthe scattering of the debris produced upon irradiating one side face(planar surface) of the rotating element 1 with the energy beam 6′. Theconfiguration shown in FIG. 6A, on the other hand, only allows thedebris to proceed into the chamber 20 through the opening 11. Therefore,it is possible to suppress the diffusion (dispersion) of the debris byproperly deciding the size of the opening 11.

Suppressing Scattering of High Temperature Plasma Raw Material (3)

It should be noted that if the scattering of the liquid high temperatureplasma raw material 23 from the opening 11 should further be suppressed,the liquid high temperature plasma raw material 23 applied on therotating element 1 may be cooled in a region, which is irradiated withthe energy beam 6′ passing through the opening 11, and its neighboringregion such that the liquid high temperature plasma raw material 23 issolidified. This can further suppress the scattering of the hightemperature plasma raw material 23 into the plasma space (chamber 20)from the opening 11. When the solid-phase high temperature plasma rawmaterial 23 is irradiated with the energy beam 6′ and the EUV light isemitted, the surface of the solid-phase high temperature plasma rawmaterial 23 on the rotating element 1 deforms. However, when thesolid-phase deformed region passes through the first reserving vessel 4upon the rotation of the rotating element 1, this region is transformedto the liquid-phase again. Then, the liquid high temperature plasma rawmaterial 23 is applied again on this surface. In this manner, thesurface is regenerated.

A unit for cooling and solidifying the liquid high temperature plasmaraw material 23 may be provided, for example, in the following manner.The film thickness controlling mechanism 5 may be disposed in thevicinity of the opening 11, and a cooler function or module (not shown)may be imparted to the film thickness controlling mechanism 5.Specifically, a cooling mechanism that uses a cooling water or the likemay be disposed behind the film thickness controlling mechanism 5 in therotating direction of the rotating element 1. Alternatively, a mechanismfor spraying a noble gas (e.g., helium or argon) to the high temperatureplasma raw material may be disposed behind the film thicknesscontrolling mechanism 5. Such mechanism solidifies the liquid hightemperature plasma raw material 23, with its film thickness beingcontrolled.

Improving Application Property of High Temperature Plasma Raw Material(1)

In the examples shown in FIGS. 1A and 6A, the proceeding direction ofpart of the rotating element 1 into the liquid high temperature plasmaraw material 23 is substantially perpendicular to the surface (liquidsurface) of the liquid high temperature plasma raw material 23. However,the present invention is not limited in this regard. For example, asshown in FIG. 7, the rotating element 1 may be inclined relative to theliquid surface direction (gravity direction) of the high temperatureplasma raw material 23, and the incident angle of the rotating element 1to the liquid surface of the liquid high temperature plasma raw material23 may become an oblique angle. Specifically, the rotation center shaft3 of the rotating element 1 may be inclined relative to the direction ofthe normal line to the liquid surface of the high temperature plasma rawmaterial 23 such that an amount of dripping (dropping) of the liquidhigh temperature plasma raw material 23 may be reduced, as compared tothe examples shown in FIGS. 1A and 6A. This ensures that the liquid hightemperature plasma raw material 23 is applied onto part of the surfaceof the rotating element 1 in a more reliable manner. Thus, it ispossible to further facilitate the lifting up of the liquid hightemperature plasma raw material 23 upon the rotation of the rotatingelement 1.

Improving Application Property of High Temperature Plasma Raw Material(2)

As described above, the high temperature plasma raw material 23 isapplied onto the surface of the rotating element 1 as part of therotating element 1 is immersed in the liquid high temperature plasma rawmaterial 23 reserved in the first reserving vessel 4. The hightemperature plasma raw material 23 is then conveyed to the region to beirradiated with the energy beam 6′. Thus, it is preferred that theliquid high temperature plasma raw material 23 has a good contact withthe surface of the rotating element 1. In other words, it is preferredthat the surface of the rotating element 1 has a good wettability to theliquid high temperature plasma raw material 23.

In general, however, the rotating element 1, which is made from a highmelting point metal such as molybdenum, does not have a good contactproperty to the liquid high temperature plasma raw material 23.

In such case, a surface texturing process may be applied on the surfaceof the rotating element 1. By applying the surface texturing process tothe surface of the rotating element 1, the surface of the rotatingelement 1 has an improved wettability to the liquid high temperatureplasma raw material 23. Thus, the surface of the rotating element 1 hasa better contact with the liquid high temperature plasma raw material23, and the liquid raw material is applied onto the rotating element 1in a more reliable manner.

Improving Application Property of High Temperature Plasma Raw Material(3)

Instead of applying the surface texturing process, there may be provideda mechanism for carrying out the surface reforming (modification) on thesurface of the rotating element 1 with the plasma, which is generatedupon discharge, irradiation of a laser beam, irradiation of an ion beam,irradiation of an electron beam or the like, in order to improve theapplication property of the rotating element 1.

For example, a substance (e.g., oxide) that adheres onto the surface ofthe rotating element 1 and can deteriorate the wettability of the liquidhigh temperature plasma material (tin) may be removed by the plasma ofthe discharging process (sputtering) or the like, in order to enhancethe reactivity between the material of the rotating element 1 and tin(high temperature plasma raw material 23) and improve the surfacetension of tin. This in turn causes the rotating element 1 to have abetter wettability to tin.

FIG. 8 shows a configuration that carries out the surface reforming tothe surface of the rotating element 1 with the discharge M.

As illustrated in FIG. 8, an electrode 33 faces the surface of therotating element 1 via the opening 11 formed in the cover-like structure2. A power source device (e.g., high voltage pulse power source or ahigh voltage high frequency AC power source) 34 is then connected to theelectrode 33 and the cover-like structure 2. The rotating element 1 iselectrically connected to the power source device 34 via the hightemperature plasma raw material 23 reserved in the cover-like structure2 (i.e., in the first reserving vessel 4).

The discharge M is generated between the electrode 33 and the rotatingelement 1 by applying a high voltage across the electrode 33 and therotating element 1 from the power source device 34. Thus, the surface ofthe rotating element 1 is exposed to the discharge M, and the oxide andother substances in that surface region of the rotating element 1 wherethe discharge M is generated are removed. Accordingly, it is possible toproperly apply the liquid high temperature plasma raw material 23 inthat region.

As described above, the electrode 33 faces the surface of the rotatingelement 1 through the opening 11 formed in the cover-like structure 2.Thus, that region on the rotating element 1 which is surface-reformed bythe discharge M is a region to be irradiated with the energy beam 6′ viathe opening 11.

It goes without saying that the surface reforming to the surface of therotating element 1 by the discharge M is performed before the rotatingelement 1 is irradiated with the energy beam 6′. As the rotating element1 is caused to rotate during the discharge, that region of the rotatingelement 1 which is irradiated with the energy beam 6′ is entirelysurface-reformed. It is needless to say that the region of the rotatingelement 1, which is irradiated with the energy beam 6′, is an annularregion.

When the surface treatment with the discharge M finishes, the electrode33 is retracted from the opening 11 of the cover-like structure 2 by adrive mechanism (not shown) such that the electrode 33 is moved to aposition that does not obstruct (block) the radiating (travelling) pathof the energy beam 6′ to the rotating element 1.

It should be noted that a second opening may be formed in the cover-likestructure 2, which is separate from the opening 11, and the electrode 33may face the surface of the rotating element 1 through the secondopening. In this configuration, the electrode 33 does not block thetravelling of the energy beam 6′ to the rotating element 1, andtherefore it is not necessary to move the electrode 33 with the drivemechanism or the like.

The position of the second opening in the cover-like structure 2 is aposition that faces the annular region of the rotating 1, which isirradiated with the energy beam 6′. This position of the second openingallows the provision (arrangement) of the electrode 33.

Improving Application Property of High Temperature Plasma Raw Material(4)

As described above, that region of the rotating element 1 which isirradiated with the energy beam 6′ is the annular region. Thus, a groove12 may be formed in the surface of the rotating element 1 such that thegroove 12 corresponds to the annular region.

FIGS. 9A and 9B show an embodiment that has an annular groove 12 in thesurface of the rotating element. FIG. 9A illustrates the rotatingelement 1 when viewed from the direction of the rotation center shaft 3of the rotating element 1. FIG. 9B is a cross-sectional view taken alongthe line E-E in FIG. 9A. FIG. 9B also illustrates the cover-likestructure 2.

As depicted in FIGS. 9A and 9B, the groove 12 is formed, in an annularshape, in the side face (planar surface) of the rotating element 1.Because the groove 12 is provided, the liquid high temperature plasmaraw material 23 is applied such that the liquid high temperature plasmaraw material 23 retains in the groove 12. Thus, it is possible to conveythe liquid high temperature plasma raw material 23 to the region, whichis irradiated with the energy beam 6′, in a more reliable manner uponthe rotation of the rotating element 1. It should be noted that theabove-described surface texturing process or the surface treatment maybe applied to the groove 12.

It should be noted that the groove does not necessarily extend coaxiallyand continuously as described above. For example, as shown in FIG. 10,the groove may be provided discretely (intermittently).

FIG. 10 depicts the side face (planar surface) of the rotating element1. FIG. 10 shows a plurality of recesses 12 a that are discretely andannularly disposed around the rotation center of the rotating element 1.Instead of the recesses 12 a, there may be provided a plurality ofthrough holes discretely and annularly around the rotation center of therotating element 1. The through holes can also retain the liquid hightemperature plasma raw material 23 therein because of the surfacetension. Therefore, similar to the configuration having the groove orthe like, it is possible to convey the high temperature plasma materialto a region to be irradiated with the energy beam 6′.

Mechanism for Circulating High Temperature Plasma Raw Material

Referring back to FIG. 1A, that part of the liquid high temperatureplasma raw material 23 applied on part of the rotating element 1, whichis irradiated with the energy beam 6′, is consumed. As the rotatingelement 1 rotates, that region of the rotating element 1 where said partof the high temperature plasma raw material 23 is consumed is returnedto the first reserving vessel 4, and the high temperature plasma rawmaterial 23 is supplemented to the region where said part of the hightemperature plasma raw material 23 has been consumed such that the rawmaterial is conveyed again upon the rotation of the rotating element 1.As such, the high temperature plasma raw material 23 is circulated tothe region irradiated with the energy beam 6′.

On the other hand, the liquid high temperature plasma raw material 23(tin) is circulated between the first reserving vessel 4 and the secondreserving vessel 7 a by the liquid raw material circulating device 7.

The liquid raw material circulating device 7 includes the secondreserving vessel 7 a for reserving (storing) the high temperature plasmaraw material 23, raw material inflow and outflow conduits 7 b and 7 cfor circulating the high temperature plasma raw material 23 between thefirst reserving vessel 4 and the second reserving vessel, and a rawmaterial drive unit (pump) 8 for circulating the plasma material.

The raw material inflow conduit 7 b is connected to the first reservingvessel 4 to introduce the high temperature plasma raw material 23 to thefirst reserving vessel 4 from the second reserving vessel 7 a, and theraw material outflow conduit 7 c is connected to the first reservingvessel 4 to allow the high temperature plasma raw material 23 to flowout of the first reserving vessel 4 and flow to the second reservingvessel 7 a.

In order to stably perform the EUV radiation for a long time, it ispreferred that a large amount of high temperature plasma raw material 23is reserved in the first reserving vessel 4. However, when the size ofthe chamber 20 of the EUV light source device is considered, there is alimitation on the size of the first reserving vessel 4 mounted(supported) in the chamber 20. Thus, it is difficult to store a largeamount of tin in the first reserving vessel 4.

To cope with this, this embodiment includes the second reserving vessel7 a outside the chamber 20. The second reserving vessel 7 a isconfigured to reserve a large amount of high temperature plasma rawmaterial 23 (e.g., liquid tin) therein. Thus, this embodiment cansupplement the high temperature plasma raw material 23 to the firstreserving vessel 4 via the raw material inflow conduit 7 b. Thisconfiguration ensures that a constant (desired) amount of hightemperature plasma raw material 23 is stored in the first reservingvessel 4 for a long time. As a result, it is possible to stably carryout the EUV radiation for a long time.

As described above, the raw material inflow conduit 7 b for receivingthe high temperature plasma raw material from the second reservingvessel 7 a is connected to the first reserving vessel 4, and the rawmaterial outflow conduit 7 c for allowing the high temperature plasmaraw material 23 to flow out of the first reserving vessel 4 toward thesecond reserving vessel 7 a is also connected to the first reservingvessel 4. Thus, the high temperature plasma raw material 23 iscirculated between the first reserving vessel 4 and the second reservingvessel 7 a such that an amount of high temperature plasma raw material23 in the first reserving vessel 4 becomes constant or a desired amount.

As the high temperature plasma raw material 23 applied on part of therotating element 1 is irradiated with the energy beam 6′, the hightemperature plasma is produced and the EUV radiation takes place. At thesame time, the rotating element 1 itself is heated. The heated rotatingelement 1 performs the heat exchange between the high temperature plasmaraw material 23 and the rotating element every time the rotating element1 passes through the interior of the first reserving vessel 4, whichreserves the high temperature plasma raw material 23. Thus, if the hightemperature plasma raw material 23 reserved in the first reservingvessel is not circulated, the temperature of the high temperature plasmaraw material 23 in the first reserving vessel 4 changes. When the hightemperature plasma raw material 23 is a liquid tin, the viscosity of theliquid tin changes with the temperature. Thus, the wettability of therotating element 1 to the liquid tin also changes, and the contactcondition of the liquid tin with the rotating element 1 also changes.Accordingly, there is a possibility that the output of the EUVradiation, which is generated when the high temperature plasma rawmaterial 23 applied on part of the rotating element 1 is irradiated withthe energy beam 6′, may also change.

If the second reserving vessel 7 a, which has a relatively large size,is disposed outside the chamber 20 of the EUV light source device, andthe high temperature plasma raw material 23 is circulated between thefirst reserving vessel 4 and the second reserving vessel 7 a, then alarge(r) amount of high temperature plasma raw material 23 (liquid tin)can be stored in the second reserving vessel 7 a, and therefore it ispossible to make the heat capacity of the liquid tin large(r). As such,even if the liquid tin that has changed its temperature in the firstreserving vessel 4 flows in the second reserving vessel 7 a through theraw material outflow conduit 7 c, the temperature of the liquid tin inthe second reserving vessel 7 a does not change very much, i.e., thetemperature of the liquid tin in the second reserving vessel 7 a is keptto a substantially fixed value. Because the liquid tin that has thesubstantially fixed temperature flows in the first reserving vessel 4through the raw material inflow conduit, the temperature of the liquidtin in the first reserving vessel 4 is also kept to a substantiallyfixed value. Therefore, the adhesion (contact) of the liquid tin ontothe rotating element 1 becomes stable, and the output of the EUVradiation also becomes stable.

The temperature of the high temperature plasma raw material 23 in thesecond reserving vessel 7 a is adjusted (regulated) by a temperatureadjusting mechanism 7 d disposed in the second reserving vessel 7 a.Because the second reserving vessel 7 a is disposed outside the chamber20, it is possible to use the temperature adjusting mechanism 7 d havinga large capacity, independent of the size of the chamber 20. Thus, it ispossible to set the temperature of the high temperature plasma rawmaterial 23 (liquid tin) to a predetermined temperature in a short time.

For example, when the high temperature plasma raw material 23 is theliquid tin, the above-mentioned predetermined temperature is atemperature that can maintain tin in the liquid phase. In other words,the temperature control is performed such that the tin, which is thehigh temperature plasma raw material 23, is maintained at a temperatureequal to or higher than the melting point. It should be noted that anexcessive temperature elevation of the high temperature plasma rawmaterial 23 (liquid tin) accelerates the deterioration of the structuresuch as the first reserving vessel 4 and the second reserving vessel 7a. Therefore, the controlled temperature is preferably set to near themelting point of the high temperature plasma raw material 23 (tin).

It is preferred that that face of the liquid tin circulating device 7which contacts the liquid material, that face of the first reservingvessel 4 which contacts the liquid material, that face of the rawmaterial inflow conduit 7 b which contacts the liquid material, thatface of the raw material outflow conduit 7 c which contacts the liquidmaterial, and that face of the cover-like structure 2 which contacts theliquid material are coated with a ceramic material (e.g., TiN)respectively to prevent erosion, which would otherwise be caused by theliquid metal. Alternatively, it is preferred that that face of theliquid tin circulating device 7 which contacts the liquid material, thatface of the first reserving vessel 4 which contacts the liquid material,that face of the raw material inflow conduit 7 b which contacts theliquid material, that face of the raw material outflow conduit 7 c whichcontacts the liquid material, and that face of the cover-like structure2 which contacts the liquid material are made from a metal having a highmelting point (e.g., tungsten, molybdenum, or tantalum) and/or itsalloy.

The circulation of the high temperature plasma raw material 23 betweenthe first reserving vessel 4 and the second reserving vessel 7 a isperformed by the raw material drive unit 8. The raw material drive unit8 includes, for example, an electromagnetic pump to convey the liquidmetal by means of a magnetic force.

Specifically, the liquid raw material circulating device 7 uses theelectromagnetic force of the raw material drive unit 8, i.e., theelectromagnetic pump, to convey the liquid tin, i.e., the hightemperature plasma raw material 23, to the first reserving vessel 4 fromthe second reserving vessel 7 a through the raw material inflow conduit7 b. Part of the high temperature plasma raw material 23 reserved in thefirst reserving vessel 4 is applied, in the form of thin film, onto partof the surface of the rotating element 1 upon rotation of the rotatingelement 1. Part of the applied high temperature plasma raw material 23is excited by the pulse laser beam (i.e., the energy beam 6′).Accordingly, the high temperature plasma is generated, and the EUVradiation takes place. That region of the rotating element 1, in whichthe high temperature plasma raw material 23 is applied, includes aregion irradiated with the energy beam 6′ and returns to the firstreserving vessel 4 again upon the rotation of the rotating element 1.Thus, the high temperature plasma raw material 23 is supplemented to theregion where the high temperature plasma raw material 23 is consumed(disappears) upon irradiation of the energy beam 6′. It should be notedthat the high temperature plasma raw material 23 reserved in the firstreserving vessel 4 returns to the second reserving vessel 7 a throughthe raw material outflow conduit 7 c due to the gravity and theelectromagnetic force. The temperature of the high temperature plasmaraw material becomes the predetermined value in the second reservingvessel 7 a, and the high temperature plasma raw material 23 iscirculated again to the first reserving vessel 4.

If a certain abnormality occurs in the liquid raw material circulatingdevice 7, and the circulation of the high temperature plasma rawmaterial 23 between the first reserving vessel 4 and the secondreserving vessel 7 a stops, then there is a possibility that the hightemperature plasma raw material 23 moves to the first reserving vessel 4from the second reserving vessel 7 a if the liquid surface of the liquidhigh temperature plasma raw material in the second reserving vessel 7 ais higher than the liquid surface of the liquid high temperature plasmaraw material in the first reserving vessel 4 when viewed in the gravitydirection. As described above, the second reserving vessel 7 a stores alarger amount of high temperature plasma raw material 23 than the firstreserving vessel 4. Also, the cover-like structure 2 that serves as thefirst reserving vessel 4 has the opening 15, 11 to direct the energybeam 6′ to the rotating element. Thus, if the high temperature plasmaraw material 23 moves, there is a possibility that the high temperatureplasma raw material 23 overflows the first reserving vessel 4, and theliquid high temperature plasma raw material 23 flows into the chamber20, i.e., the plasma generating space.

Therefore, it is preferred that the first reserving vessel 4 and thesecond reserving vessel 7 a are arranged such that the liquid surface ofthe liquid high temperature plasma raw material in the second reservingvessel 7 a of the liquid raw material circulating device 7 is lower thanthe liquid surface of the liquid high temperature plasma raw material inthe first reserving vessel 4 when viewed in the gravity direction.

The second reserving vessel 7 a is a closed space. Thus, the secondreserving vessel 7 a receives and stores the surplus liquid hightemperature plasma raw material 23, which flows in from the firstreserving vessel 4, without leakage of the raw material 23 to theoutside.

Although specific embodiments of the present invention are described inthe foregoing, these embodiments are mere examples, and do not intend tolimit the scope of the present invention. The device (apparatus) and themethod described in the specification may be practiced in differentforms and embodiments from the above-described embodiments. It is alsopossible to make omissions, substitutions, changes and/or modificationsto the above-described embodiments, if necessary, without departing fromthe scope of the invention. Those embodiments which are obtained afterthe omissions, substitutions, changes and/or modifications areencompassed by the claims and their equivalents, i.e., such embodimentsfall in the technical scope of the present invention.

This application is based on Japanese Patent Application No. 2013-95235(filed on Apr. 30, 2013), and claims a priority from theabove-identified Japanese Patent Application. The entire disclosure ofthe above-identified Japanese Patent Application is incorporated hereinby reference.

REFERENCE NUMERALS AND SIGNS

-   -   1: Rotating element    -   2: Cover-like structure    -   3: Rotation center shaft    -   4: First reserving vessel    -   5: Film thickness controlling mechanism    -   5 a: Block-like structure    -   5 b: Plate-like structure    -   5 c: Structure having a channel-like recess    -   5 d: Channel-like recess    -   6: Energy supplying mechanism (laser radiation device)    -   6′: Energy (laser) beam    -   7: Liquid raw material circulating device    -   7 a: Second reserving vessel    -   8: Raw material drive (pump)    -   9: Scattering preventing structure    -   10: Flying particles    -   11: Opening    -   12: Groove    -   12 a: Recess    -   13: Motor    -   13 a: Motor rotation shaft    -   14: Mechanical seal    -   15: Opening    -   16: Coupling    -   20: Chamber    -   21: Foil trap    -   22: EUV light condensing mirror    -   23: High temperature plasma raw material    -   30: Exposure device    -   33: Electrode    -   34: Power supply device

1. An extreme ultraviolet light source device comprising: a disc-like rotating element; a rotation unit configured to cause the rotating element to rotate about a rotation center shaft, which is perpendicular to a single flat surface of the rotating element; a cover-like structure configured to surround the rotating element with a gap; a first reserving vessel disposed in the cover-like structure and configured to reserve a liquid high temperature plasma raw material, with part of the rotating element being immersed in the high temperature plasma raw material reserved in the first reserving vessel; a raw material supplying mechanism configured to apply the liquid high temperature plasma raw material onto at least part of the single flat surface of the rotating element upon a rotating movement of the rotating element; an energy beam providing device configured to irradiate the high temperature plasma raw material with an energy beam; and a film thickness controlling mechanism provided in the cover-like structure, the film thickness controlling mechanism including a U-shaped structure having a channel-like recess, the U-shaped structure being biased by an elastic body in a direction against the single flat surface of the rotating element such that two opposite sides of the U-shaped structure contact the single flat surface of the rotating element, a clearance between the rotating element and a bottom of the recess of the structure, which faces the rotating element, being set such that the liquid high temperature plasma raw material applied on the rotating element has a predetermined film thickness, the cover-like structure of the raw material supplying mechanism having an opening in a certain part of the cover-like structure such that the energy beam is directed to the single flat surface of the rotating element, on which the high temperature plasma raw material is applied, through the opening of the cover-like structure, and extreme ultraviolet light generated upon irradiation of the energy beam is released from the opening of the cover-like structure, the cover-like structure having a scattering preventing member disposed to oppose a direction of a centrifugal force acting on the rotating element, which is caused to rotate by the rotation unit, and cover the rotating element.
 2. The extreme ultraviolet light source device according to claim 1, wherein a groove, a recess or a through hole is formed in at least that face out of two faces of the disc-like rotating element which is irradiated with the energy beam, the two faces of the rotating element being perpendicular to the rotation center shaft of the rotating element.
 3. The extreme ultraviolet light source device according to claim 1 further comprising: an electrode that faces at least one of two faces of the disc-like rotating element in a region irradiated with the energy beam, the two faces of the rotating element being perpendicular to the rotation center shaft of the rotating element; and a power source device for applying a voltage across the electrode and the rotating element.
 4. The extreme ultraviolet light source device according to claim 1 further comprising a liquid raw material circulating device, the liquid raw material circulating device including a second reserving vessel configured to reserve the high temperature plasma raw material, a raw material inflow conduit connected between the second reserving vessel and the first reserving vessel and configured to allow the high temperature plasma raw material to flow in the first reserving vessel from the second reserving vessel, a raw material outflow conduit connected between the second reserving vessel and the first reserving vessel and configured to allow the high temperature plasma raw material to flow in the second reserving vessel from the first reserving vessel, and a raw material drive unit configured to convey the high temperature plasma raw material to the first reserving vessel from the second reserving vessel.
 5. The extreme ultraviolet light source device according to claim 1, wherein the energy beam directed to the flat surface of the rotating element onto which the high temperature plasma raw material is applied is a laser beam.
 6. The extreme ultraviolet light source device according to claim 1, wherein the energy beam directed to the flat surface of the rotating element onto which the high temperature plasma raw material is applied includes two laser beams. 